Many electronic systems require the provision of DC (direct current) electrical power. Colloquially speaking, DC power involves the flow of electrical current in a constant direction, from a high voltage (i.e., electrical potential) to a low voltage. (In AC—alternating current—power applications, the magnitude and direction of the electrical current vary cyclically.) DC distribution systems are used to provide DC power to electronic circuits and devices that require DC power to operate. As such, DC distribution systems typically perform one or more of the following functions: convert an AC source to a DC waveform; regulate and/or transform the converted DC waveform into a more desired form, e.g., different voltage levels, or a purer DC waveform; and monitor and control the input and/or output power waveforms for safety and/or other control purposes.
High power DC supply systems perform similar functions, but are used in electronics applications requiring large amounts of DC electrical power. For example, in commercial and government wireless telecommunication systems, RF (radio frequency) amplifiers and other high power electronics are used for amplifying voice and data signals for long distance wireless transmission. The amplifiers are housed in a frame or other support assembly, which includes a DC panel board having input and output power lines/buses, supply/filter/bypass capacitors, and banks of circuit breakers. In a typical frame, the electronic devices housed therein might require DC power at the level of hundreds of amperes of current and thousands of watts.
Because of the high voltage and/or current levels involved, high power DC distribution systems require robust, high-capacity components, and in some applications a more robust monitoring and protection scheme. For example, certain applications may require over-voltage safeguards (e.g., protection for situations where an input/source voltage increases significantly), under-voltage safeguards (e.g., protection for situations where an input/source voltage drops or is removed), circuit breaker functionality, and current inrush protection. Regarding the latter, when DC power systems are first activated, high levels of transient current may be generated as a result of capacitor impedance. Large filter and storage capacitors act like a short circuit, producing an immediate inrush surge current with a fast rise time. The peak inrush current may be several orders of magnitude greater than the circuit's steady state current level. This power surge can seriously damage system components, and may result in blown fuses and tripped circuit breakers.
Traditionally, current inrush protection has been provided by way of a large, high-capacity resistor. First, the resistor charges the storage/filter capacitors. Then, the resistor is shorted using a high-current relay. Although such circuits are functional, they are quite bulky, and the resistor may fail if the load is shorted. Moreover, there are no provisions for low and high voltage dropout, e.g., over-voltage and under-voltage safeguards.